In my world, I've cleared out an entire chunk, from bedrock to about 90 (ground level). It is a slime chunk, and slimes are spawning in the bottom. At level 40, I constructed several hostile mob spawning pads. They are dark, and have a large enough area for mobs to spawn. But the strange thing is, they're not spawning at all. During construction of the pads, there were a couple of skeletons, zombies, and a creeper, but nothing near what you'd expect from an entire empty chunk. There are no slimes preventing spawning, and I've AFK'd for quite a while beyond 24 blocks from the pads.
So my question is, do normal hostile mobs (zombies, etc) not spawn in slime chunks?